This invention relates to valve apparatus, and more particularly to the class of valves commonly known as positive end expiratory pressure devices.
Positive end expiratory pressure (PEEP) has become a mainstay in the treatment of patients with respiratory failures. In such treatment, there is provided a carefully structured and controlled back pressure to the patient, thereby forcing the patient to exert a clinically desirable amount of respiratory effort. Typically, regulation of the pressure characteristics of the PEEP device allows for progressive, increases of lung effectiveness and capacity of the patients.
Increasing use of PEEP devices and therapy has yielded rather sharp performance requirements, not only from the primary standpoint of effectiveness and safety to the patient, but also with respect to ease and convenience of use. From the standpoint of patient effectiveness and safety, it is desirable that PEEP devices provide for a broad pressure range, including relatively high pressures in the 20 to 30 centimeters H.sub.2 O range, without impairment of effectiveness at any given operating point. Further, it is desirable that the pressure characteristics of the device be relatively independent of the air flow rate, such that the therapy may be utilized even with patients with severe pulmonary disfunction. Equally important, the valve response time to exerted pressure changes should be as quick as possible, to avoid transmittal back of undue transient pressures to the patient, and vibration and flutter of the pressure are to be similarly avoided. With respect to convenience and ease of use, it is desirable that the apparatus be sterilized easily, provide as close to infinite adjustability as possible, and allow for simple and accurate determination by the doctor or therapist of the current operational condition of the device.
The present invention has as its primary objects provision of positive end expiratory pressure devices which satisfy the above considerations as closely as possible. It is a further object of the present invention to provide such devices which may be conveniently used separately as a ventilator on constant flow circuits commonly known as constant positive air way pressure (CPAP) apparatus.